Molecular weight control of polymers



United States Patent 3,423,379 MOLECULAR WEIGHT CONTROL OF POLYMERS Lowell D. Grinninger and Harry Greenberg, Cincinnati, Ohio, assignors to National Distillers and Chemical Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Nov. 14, 1966, Ser. No. 593,629 US. Cl. 260--82.1 claims Int. Cl. C08f 1/56, ]/28 ABSTRACT OF THE DISCLOSURE A process is provided for control of the molecular weight of alifin polymers and copolymers by carrying out the polymerization in the presence of an alfin catalyst and an allylbenzene compound, an allylnaphthalene compound, or mixtures thereof as a molecular weight modifier.

This invention relates to a process for the controlled ;polymerization of unsaturated organic compounds and, more particularly, to an improved process for the proiduction of polymers and copolymers of unsaturated or- }ganic compounds, said polymers and copolymers having controlled molecular weights. Specifically, the invention provides a new class of compounds capable of functioning as molecular weight control agents in the production of polymer products by polymerizing or copolymerizing unsaturated organic compounds in the presence of an alfin catalyst.

The polymerization of unsaturated organic compounds, e.g., ethylenically unsaturated compounds such as conjugated diolefins including 1,3-butadiene, with or without comonomers such as vinyl aromatics including styrene, in the presence of an alfin catalyst, as defined hereinafter, is known. The use of an alfin polymerization catalyst results in an unusually rapid rate of reaction and in good yields of polymer. In comparison with synthetic rubbers made by conventional catalytic polymerizing techniques, the alfin rubbers are generally gel-free and have higher flex-life values, high tensile strength, superior abrasion resistance and tear strength. Alfin rubbers however, have the disadvantage of being characterized by extremely high molecular weights, i.e., 5,000,000 and over as indicated by viscosity measurements. Because of such high molecular weights, these rubbers are very tough and exhibit little breakdown and extremely poor banding on being milled. They are, therefore, very difficult to process using conventional equipment and conventional procedures, and attempts to mill and compound them result in very rough stocks with relatively high shrinkage and exceedingly high viscosities. Attempts to obtain an alfin rubber of lower molecular weight by regulating the polymerization have proved unsuccessful, and so, until now, alfin rubbers have ben commercially unattractive.

More recently, process modifiers have been discovered which have the cumulative effect of modifying the process of the polymer formation to give molecular weight controlled alfin polymers. Recently issued US. Patent No. 3,067,187 discloses a .process for controlling the molecular weights of alfin catalyzed polymers which comprises carrying out the polymerization in the presence of certain dihydro derivatives of aromatic hydrocarbons which include 1,4-dihydrobenzene, 1,4-dihydronapthalene, 1,2-dihydrobenzene, dihydrotoluene, and dihydroxylene, and the like, and mixtures of these, with 1,4-dihydrobenzene and 1,4-dihydronaphthalene being preferred.

In accordance with the present invention, a new class of compounds has been discovered which is useful for the controlled polymerization of unsaturated organic monomeric materials and mixtures of unsaturated organic monomeric materials either with or without other organic ctlamtpounds copolymerizable therewith, with an alfin cata ys Specifically, it has been discovered that an elastomer havlng controlled molecular Weight can be prepared by polymerizing an unsaturated organic compound, such as 1,3-butadiene or a mixture of an unsaturated organic compound and an organic compound copolymerizable therewith, such as styrene, using an alfin catlyst where the polymerization is carried out in the presence of a suitable molecular weight control agent comprising an allylbenzene or an allylnaphthalene, as described more fully hereinafter. The addition of controlled quantities of such a molecular weight control agent to solutions of an unsaturated organic compound such as l,3-butadiene containing an alfin catalyst gives molecular weights controlled to about 2,000,000 or less, for example controlled molecular weights as low as 50,000 or lower may be obtained. The polymer products so produced have lower intrinsic viscosities than do those made with alfin catalysts but without the use of the molecular weight control agents.

The use of an allybenzene or an allylnaphthalene molecular weight control agent does not change the ratio of 1,4-trans to 1,2-isomers in the resultant polymers, the ratio in the range of 2 to 3 in normal alfin rubbers being retained.

Any allylbenzene or allylnaphthalene compound which does not contain a substituent which would destroy the activity of the alfin catalyst may be used as a molecular weight control agent in accordance with the present invention.

Examples of allybenzenes and allylnaphthalenes useful in the present invention include but are not limited to allybenzene, both 1- and 2-allylnaphthalene, the allyltoluenes, 4-allyldiphenyl, the allylxylenes, the allylterphenyls, allylanthracene, allylphenanthrene, alkyl ethers of allyl benzenes and allylnaphthalenes wherein the alkyl group contains 1 to 12 carbon atoms such as allylanisoles, allylveratoles, dialkoxy allylbenzenes and the like. Compounds having more than one allyl group in the aromatic nucleus such as 1,4-diallylbenzene are useful. Mixtures of the various allyl compounds can also be employed. Of this series of compounds allylbenzene is the most elfective and has been found to be the most readily available.

The amount of molecular weight control agent needed or any particular level of molecular weight control is in inverse proportion to its level of moderator activity. Also the amount of molecular Weight control agent required for a given polymer molecular weight is dependent upon such factors as the temperature and pressure of the reaction and the quantity and type of diluents employed. In general, the amount of the agent used may vary from about one to about eighty percent, based on the weight of polymerizable monomer, with the use of about 1.5 to about 6 percent being most common.

In the practice of one embodiment of the present invention, the reactor is dried, flushed, and blanketed with an inert gas such as nitrogen or argon, and a dry inert hydrocarbon diluent and the molecular weight control agent are introduced. The reactor is then cooled to about 5 to -20 C., preferably to l0 C., the flow of inert gas is diverted, and dry monomer or mixture of monomer and comonomer is condensed into the diluent. Alfin catalyst is then charged into the cold diluent-monomer mixture; the reactor is sealed and shaken vigorously. After about two hours the catalyst is destroyed with ethanol and the polymer is withdrawn. It is then washed with an alcohol, such as methanol or ethanol, to remove the diluent and with water to remove soluble inorganic salt residues; and dried.

In another embodiment of this invention all of the ingredients except the monomer, that is, the diluent, alfin catalyst, and the molecular weight control agent, are introduced into the reactor. A controlled flow of monomer is then fed into the system over a period of about five gen or argon, the alfin catalyst appears to be stable almost indefinitely.

The polymerization or copolymerization reaction generally takes place at atmospheric pressure and room temperature in a suitable selected reaction medium. The preshours. This system results in greater utilization of the 5 sure and temperature conditions, however, are not crimolecular weight control agent than the former system, tical, the reaction occurring at any pressure between about i.e. because of the extended time of reaction, less mole- 1 atmosphere and about 50 atmospheres and at any temcular weight control agent is required to produce a polyperature between about 25 and 60 C. or higher. The mer of a given molecular weight. reaction medium is suitably an inert hydrocarbon, ex-

Where removal of water-soluble residues is not desired, amples including pentane, hexane, a 1:1 mixture of the catalyst can be neutralized, e.g., with acetic acid or hexane and pentane, cyclohexane, decalin, heptane, hydrochloric acid, and the diluent removed by distillabranched chain saturated hydrocarbons and the like, or tion while stirring. If desired, before diluent removal mixtures thereof, with hexane and pentane being preferred. the polymer may be compounded with any or all of the The rigorous exclusion of water from solvents, monomer, conventional vulcanization or other additives, such as and apparatus is essential. carbon, zinc oxide, stearic acid, an accelerator, and sulfur, The process may be conducted in a batchwise, semiso that the product obtained after diluent removal reprecontinuous or continuous manner, and the polymers and sents a completed formulation ready for vulcanization, copolymers so produced may be recovered by any of thus bypassing the usual milling and mixing steps. the conventional techniques.

The process of this invention is particularly well The more detailed practice of the invention is illusadapted to the polymerization of butadiene itself, i.e., 1,3- trated by the following examples wherein parts are given butadiene, and to the copolymerization of 1,3-butadiene by weight unless otherwise specified. These examples and and styrene or isoprene and will be particularly discussed embodiments are illustrative only, and the invention is with reference to such homopolymers and copolymers. not intended to be limited thereto except as indicated by The process, however, is also applicable to the formathe appended claims. The alfin catalyst used in these extion of polymers and copolymers of other unsaturated amples was prepared in accordance with the procedure organic compounds. The monomeric material polymerdescribed in U.S. patent application S.N. 271,487 filed ized in accordance with the process of this invention may Apr. 8, 1963, now Patent No. 3,317,437. include, for example, butadienes, such as 2,3-dimethyl- 3O 1,3-butadiene, isoprene, piperylene, 3-furyl-l,3-butadiene, EXAMPLEl 3-methoxy-l,3-butadiene, and the like; aryl olefins such as styrene, various alkyl Styrenes, py y a In carrying out each experiment, to 105 grams of dry Phameihylslyrene, vinylflaphthalefle, diViny1bnZn6 and commercial hexane diluent was added the amount of similar derivatives, d t like; homopolymers, p yas allylbenzene (in grns. shown) in Table I together with s, a terpolymers p p from y one or y grns. of dry 1,3-butadiene (about 99.9% purity). This combination of the above are contemplated to be within addition wa accomplished by cooling the polymerization the scope of the process of this invention. bottle containing the 105 grns. of hexane to about 20 The polymerization or copolymerization of these re- C. and condensing therein the 30 gms. of 1,3-butadiene. actants takes place i the presence f an n ly Alfill catalyst, 4ml. (0.00025 mol. allylsodium/ml.), was as that described in Patent 3,067,137, o an added to the butadiene-hexane solution. The polymeriza- 1nt1mate mixture of sodium isopropoxide, allyl sodium tion system was sealed and maintained at room temperaand sodium chloride. In general, the alfin catalyst is preture with intermittent shaking. After about two hours it pared y reacting y Chloride and Sodium in P61118116 was opened and ethanol was added to destroy the catalyst with high-speed stirring. One mole of the resulting amyl and precipitate the polymer. The polymer product was sodium suspension is then reacted with 0.5 mole of isowashed intermittently with ethanol and water containing propyl alcohol and an excess of propylene to give a mixantioxidant to remove diluent and soluble inorganic ture containing sodium isopropoxide, allyl sodium, and residues such as sodium isopropoxide and sodium chlorsodium chloride. A particularly effective alfin catalyst is ide. The resulting insoluble material was a white solid obtained when the sodium is employed as a finely divided polybutadiene. It was given a final wash with acetone dispersion, that is, a dispersion in which the average parcontaining an antioxidant, N-phenyl-Z-naphthalamine, and ticle size is about 1 to 2 microns, such as may be prethen dried in an oven at 40 C. under vacuum. Yields, pared using a Manton Gaulin mill. When such finely diintrinsic viscosities, molecular weights and microstrucvided sodium is used, ordinary stirring devices may be emtures are reported in Table I. Average molecular weights ployed instead of high-speed comminuting equipment. In were determined by preparing 0.1 and 1.0 percent soluaddition, the use of finely divided sodium results in a tions of the polymers in toluene, determing their viscossubstantially quantitative yield of amylsodium and, thereities at 25 C. and extrapolating the viscosity to infinite fore, in subsequent quantitative yields of sodium isoprodilution, and then applying standard viscosity-molecular poxide and allylsodium. Thus the alfin catalyst and conweight laws. sequently the end products of the polymerization are free Molecular weights were calculated for 25 C. using the of metallic sodium contamination. Also catalyst activity expression M =n/k where n is the intrinsic viscosity and can be more readily reproduced when finely divided k and a are constants for polybutadiene determined for sodium (about 2 micron average particle size) is used. linear polymers of known molecular weights; a is taken When maintained under an inert atmosphere, e.g., nitroas 0.62 and k as ll 10- TABLE I Allyl benzene Polymer Microstructure and Remarks Ex. No. gms./3O gms. Yield, Intrinsic Calculated Butadteue Percent Viscosity Mol. Wt. Percent, Percent, Percent,

Trans Vinyl 015 1.8 92.2 4 724, 400 67.6 27.2 5.1 3. 0 9s. 0 a. 86 537, 000 as. 2 27. s 4. 0 6.0 91.8 3.02 7.2 95.7 2. 62 4.0 82.8 2. 54 3.0 92.3 2.36

1 /20 isoprene copolymer.

835/15 styrene copolymer.

The ratio of trans to vinyl structures is 67.6/27.2 and 68.2/27.8 or 2.50 and 2.45 respectively which is in the range for true alfin polymers.

EXAMPLE 2 In another series of experiments l-allylnaphthalene was 5 substituted for allylbenzene in Example 1 with the reamount of 4-allyldiphenyl shown in the table together with 30 gms. of dry butadiene (about 99 wt. percent purity). Polymerization and a determination of physical properties were carried out in accordance with the procedures described in Example 1. Yields, intrinsic viscosities, molecular weights and microstructures are reported in the Table IV below.

sults shown in Table II. This molecular weight control agent, although not as efiective as allylbenzene, shows marked reduction in molecular weight of the resulting polymers.

TABLE II 1 allyna hthalene Polymer Intrinsic Calculated Ex. N0. gms. 30 gms. yield, viscosity molecular percent weight EXAMPLE 3 1-4-diallylbenzene was added in an amount of 0.4 gm. per gms. of 1,3-butadience dissolved in 105 gms. of commercial hexane as in Example 1. To this reaction mixture was added 4 ml. of alfin catalyst. After two hours the product was isolated as 23.1 gms. of a visibly soft polymer. The intrinsic viscosity was 4.42 which corresponds to a molecular weight of 676,100. This shows the increased effect of two allyl groups on the aromatic nucleus in controlling molecular weight.

EXAMPLE 4 In a similar experiment, 8 gms. of 4-allyltoluene was employed in a polymerization experiment where 30 gms. of 1,3-butadiene was polymerized by 4 ml. of alfin catalyst over a period of two hours. The resultant polymerization product had an intrinsic viscosity of 6.62 and a calculated molecular weight of 1,259,000. The yield was 84.5%.

EXAMPLE 5 In carrying out the experiments in Table III below, to 105 grams of dry commercial hexane was added the amount of molecular weight control agent shown in the table together with 30 gms. of dry butadiene (about 99 wt. percent purity). Polymerization and a determination of physical properties were carried out in accordance with the procedures described in Example 1. Yields, intrinsic 5 viscosities and molecular weights are reported in the Table III below.

In carrying out the experiments in Table IV below, to 105 grams of dry commercial hexane was added the What is claimed is:

1. In a process for preparing a polymer from at least one unsaturated organic monomer by polymerization of said monomer in the presence of an alfin catalyst, the improvement which comprises carrying out said polymerization in the presence of a molecular weight control agent comprising an allylbenzene, an allylnaphthalene or mixtures thereof.

2. The process of claim 1 in which the polymer is a homopolymer.

3. The process of claim 2 in which the polymer is polybutadiene.

4. The process of claim 1 in which the polymer is a copolymer containing a conjugated diolefin.

5. The process of claim 4 in which the polymer is a copolymer of 1,3-butadiene.

6. The process of claim 4 in which the polymer is a copolymer of 1,3-butadiene and styrene.

7. The process of claim 1 in which the polymer is a terpolymer.

8. The process of claim 1 in which said molecular weight control agent is present in amounts within the range of from 1 to by weight of the total weight of monomers.

9. The process of claim 1 in which said molecular weight control agent comprises allylbenzene.

10. The process of claim 1 in which said molecular weight control agent comprises l-allylnaphthalene.

11. The process of claim 1 in which said molecular weight control agent comprises allyltoluene.

12. The process of claim 1 in which said molecular weight control agent comprises an alkyl ether of an allylbenzene or an allylnaphthalene.

13. The process of claim 1 in which the polymer is a copolymer of 1,3-butadiene and isoprene.

14. The process of claim 1 in which said molecular weight control agent comprises 1,4-diallylbenzene.

15. The process of claim 1 in which said molecular weight control agent comprises 4-allyldiphenyl.

References Cited UNITED STATES PATENTS 2,008,491 7/ 1935 Ebert 260-6 3,067,187 12/1962 Greenberg et al. 260-942 3,223,691 12/1965 Greenberg et al. 260-935 JOSEPH L. SCHOFER, Primary Examiner.

I. C. HAIGHT, Assistant Examiner.

US. Cl. X.R. 

